Rectifier circuit



Patented Nov. 18, 1941 RECTIFIER CIRCUIT Clarence W. Hansel], Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 4, 1938, Serial No. 205,947

3 Claims.

This invention relates to new circuit arrangements employing mercury type rectifiers, and particularly to a method of controlling the ignition of a plurality of single-phase half-wave pool type mercury rectifiers.

A primary object of the invention is to provide a relatively simple and effective means for starting an arc discharge between anode and cathode at the required time, once per cycle of the alternating current power input.

Another object of this invention is to provide an improved and more stable rectifier system which will be less subject to frequent and objectionable backfires in a rectifier circuit.

A further object of this invention is to improve the rectifier system by sectionalizing a group of single-phase half-wave rectifiers in separate compartments, rather than to employ a single tank or compartment for accommodating a plurality of separate anodes to obtain a desired rectifier output.

Still another object of this invention is to provide an improved rectifier circuit wherein very low regulation, or decrease in output voltage with increase in load, may be obtained, together with very small output voltage ripple, for the reason that high peak currents do not injure a pool type of mercury rectifier.

In the art prior to this invention, it has been common practice to employ a plurality of anodes in the same evacuated chamber with a pool type liquid mercury cathode and to so design and operate the rectifier that the sum of the direct currents from the anodes to the cathode was above zero at all times during operation of the rectifier. The continual presence of ionization of the mercury vapor in the chamber has been a frequent cause of backfires, or fiow of currents to the anodes when their potential to the cathode was negative.

Recently, there has become available pool type rectifiers having a single anode associated with a liquid mercury cathode and with means for igniting or starting a cathode electron emitting spot on the surface of the liquid mercury. The present invention provides a novel circuit arrangement for utilizing these new types of mercury arc rectifiers and provides means for starting an are once per cycle, at the proper time, in one or more single anode rectifier tubes in an alternating current to direct current rectifier or converter.

This invention will best be understood by referring to the accompanying drawing, in which: Fig. 1 is a diagram of a three-phase rectifier employing three separate compartments; and

Fig. 2 is another circuit arrangement of the three-phase rectifier employing separate compartments.

Referring now to Fig. 1 of the drawing, there is shown an improved arrangement of this invention which is desirable for supplying resistive loads wherein each rectifier tube will carry current throughout a large portion of each positive half cycle of the alternating current. Each tube is ignited near the beginning of its positive half cycle due to the high voltage and initiation of an arc discharge at the starter a, short time before each anode and connected transformer winding is required to take over the output direct current from the next preceding tube and transformer winding taken in order of phase rotation. The transformers include primary windings 2, 3 and 4, to which are coupled secondary windings 20, 2| and 22, respectively, each of the latter having an auxiliary secondary winding 23, 24 or 25. One end of each of the secondary windings 20, 2| and 22 is connected to one side of the direct current output 26. The junction points between the main secondary and the auxiliary secondary windings of the transformers connect to separate main anodes 21, 2B and 29 of rectifiers 30, 3| and 32, each rectifier having a separate envelope containing a pool of mercury 33. The auxiliar winding 23 connects through a series resistor 34 to an arc starter or make-alive electrode 35 and the outside end of auxiliary winding 24 is connected in series with a resistance 36 to are starter 31. Likewise, the outside auxiliary winding 25 connects to series resistance 38 and are starter 39. In many cases, the operation of the system will be improved by connecting inductive reactances in series with the resistances 34, 36, 3B, or by constructing the resistances by winding resistance wire around iron cores to give them self inductance. The other side of the direct current output 40 is connected to the cathode or mercury pool 33 of each rectifier. In the operation of the system shown in Fig. 1, it may be noted, an arc is initiated by the starter, a moment later the anode main arc is established, then the starter arc goes out and a moment later the anode arc goes out, as the output current is transferred to the anode of the next rectifier tube, and the chamber becomes completely deionized. It remains completely deionized during the period of maximum inverse voltage and is not reionized until shortly before anode current is required, which is after the time of application of maximum inverse voltage. Due to the timing and absence of ionization in the chamber when the maximum inverse potential exists between anode and cathode, the probability of breakdown and establishment of an arc in a reverse direction is greatly reduced.

The circuit arrangement shown in Fig. 2 is generally similar to that of Fig. 1 but provides for ignition of each tube by potential on the starter electrode from the same phase that supplies the anode potential. Each winding between the anode and starter provides the momentary margin of potential above the direct current output potential, once per cycle of alternating current input, necessary to cause ignition while the impedance in series with the winding limits the current through the starter. This system may also be provided with smoothing condensers connected next to the tubes. High peak currents do not injure a pool rectifier, consequently, very low voltage regulation or change in voltage with ings are connected directly to anodes 5|, 52 and 53 of rectifiers 54, 55 and 56. One side 57 of the direct current output connects directly to one side of each secondary winding, the other side 58 of the direct current output being connected through a choke coil 59 to the cathode 60 of each rectifier. In shunt with the direct current output is connected a condenser 6 l Each rectifier starter 62 is connected in series with an impedance 63 to each auxiliary winding 48, 49 and 59.

Although only two circuit arrangements of this invention are shown, it is to be distinctly understood that this invention is not to be limited thereto. In practice, I will usually prefer to use two rectifier tubes per phase of alternating current input, instead of only one, as shown in the p drawing, in order to balance out the effect of direct current in magnetizing the transformer cores, to obtain less ripple in the direct current output potential, and to obtain greater power output rating. In fact, I contemplate applying my arc ignition system and circuits to any of the well known rectifier circuits.

The are starters indicated in the drawing may be short spark gaps, which I have found quite effective in initiating arcs when the vapor pressure and the potential across the gap are great enough. Alternatively, they may be an anode from which a small rod or point of resistance material projects down into the liquid mercury. The resistance material should preferably be a kind with automatically variable resistance such as Thyrite, a material originally developed by K. B. McEachron for use in lightning arresters. (See U. S. Pat. #1,822,'742.) In the latter type of starter, a small are or cathode spot starts at the junction of the surfaces of the resistance material and the liquid mercury, causing an arc to form between the mercury and the starter anode, short circuiting the resistance material. Then, the arc transfers itself first partially and then entirely to the main anode when the main anode is positive with respect to the mercury cathode.

What is claimed is:

1. An electric conversion system comprising a three phase alternating current circuit, a transformer having a primary and a secondary for each phase, a rectifier unit comprising an anode, a liquid mercury cathode and a starter electrode, all located within an envelope and associated with each secondary winding, one terminal of each secondary being connected to a direct current output bus, an intermediate point on each secondary winding being connected to the anode of the rectifier unit associated therewith, and the other terminal of each secondary being connected through a resistive connection to the starter electrode of the rectifier unit associated with the next phase, whereby each secondary is divided into two windings and the starter electrode of each rectifier unit is excited in advance of the anode of the same unit and with a predetermined magnitude of alternating current potential, and a connection from another direct current output bus to the liquid mercury cathodes of all rectifier units.

2. A mercury vapor rectifier system comprising a multi-phase alternating current input circuit and a direct current output circuit, a secondary transformer winding for each phase, a mercury vapor rectifier unit having an anode, a mercury cathode and an arc starter electrode all located within an envelope and associated with each secondary winding, an electrical connection conductive to alternating current extending from each secondary winding to the anode of the associated rectifier unit, each secondary winding having an extended portion, and a permanently conductive connection connecting the extended portion of each secondary winding to the starter electrode of the rectifier unit associated with the next phase which last unit is arranged to be supplied with anode potentials which are, later in point of time.

3. A mercury vapor rectifier system. comprising a multi-phase alternating current input circuit and a direct current output circuit, a secondary transformer winding for each phase, a mercury vapor rectifier unit having an anode, a mercury cathode and an arc starter electrode all located within an envelope and associated with each secondary winding, an electrical connection conductive to alternating current extending from each secondary winding to the anode of the associated rectifier unit, each secondary Winding having an extended portion, and a permanently conductive connection having an impedance serially connected therein ccnnecting the extended portion of each secondary winding to the starter electrode of the rectifier unit associated with the next phase which last unit is arranged to be supplied with anode potentials which are later in point of time.

CLARENCE W. HANSELL. 

